In addition to the basic events of adhesion and injection, enveloped viruses may, under particular conditions, produce a number of celluslar and molecular effects including agglutination, lysis, and polykaryocyte induction. The general objective of this proposal is to reduce the events involved in these actions of viruses to the simplest possible system and thereby to evaluate the role of each component. Viral membranes contain about six proteins and six classes of complex lipids. The host cell membranes contain the same lipids and one protein, the receptor, which is of critical importance. The number of constituents of the total system is therefore small and susceptible to individual analysis. The experiments proposed are basically reconstitution experiments in which a particular component is varied and the effect of this change on the phenomenon of interest is evaluated. Since all of the phenomena to be studied are membrane related, advantage is taken of the fact that membrane lipids themselves aggregate into bimolecular leaflets, a structure which, according to current views, obtains in biological membranes. Using the techniques described, both the viral and host cell membranes may be reconstituted with practically any desired composition. In any process by which separate membranes fuse to become one, the lipid matrix must be involved, consequently the first project has the objective of elucidating the conditions under which bimolecular layers of lipid may be caused to fuse. A second project will be aimed at the modification of the lipid membranes in such a way that they are able to carry out some of the functions of intact viruses, particularly polykaryocytosis. A third project calls for selective reconstitution of the proteins of Sendai virus into membranes and the subsequent analysis of the roles of these proteins. The final project has the objective of preparing membranes containing the virus receptor molecule as the only protein and the subsequent elucidation of the datails of virus-receptor interaction. These experiments are expected to provide information on the forces which maintain membrane integrity as well as those which are involved in membrane-membrane adhesion and will therefore be applicable to membranes in general in addition to the particular case of virsus-cell membrane interactions.